Usually, no. For most photography, the camera’s built-in meter is enough to get a good exposure recommendation.

A handheld light meter can still be useful in some cases:

• studio or flash photography, where you want to measure light very precisely
• difficult lighting scenes that may fool reflected metering in the camera
• incident metering, where you measure the light falling on the subject rather than light reflected from it
• film workflows, where checking exposure before shooting can be more important

Your camera meter measures reflected light through the lens, which is convenient and usually accurate. A handheld meter can be more consistent when the subject is very bright or very dark, or when setting up lights.

So an external meter is not necessary for most beginners or general photography, but it can be a helpful specialist tool depending on how and what you shoot.